Synthetic paper yarn



United States Patent 3,168,802 SYNTHETIC PAPER YARN William F. Linhe and Walter F. Reynolds, Stamford, Conn, assignors to American Cyanamid Company, Stamford, CGIEIL, a corporation of Maine No Drawing. Filed Nov. 27, 1962, Ser. No. 240,428 1 Clmfrn. (Cl. 57-448) The present invention relates to textile yarn substantially composed of fibrillated polyacrylonitrile papermaking fibers, and to a process for the manufacture of said yarn. It is known that synthetic paper of unique properties .can be prepared by refining an aqueous suspension ofsaid spun polyacrylonitrile filaments, sheeting the resulting suspension of fibrillated filaments to form a water-laid web, and drying the web at elevated'temperature thereby also heat-bonding the fibrils, cf. Wooding et al. US. Patent No. 2,810,646 (1957). The fibers may be composed of substantially pure polyacrylonitrile, or of a copolyrner of acrylonitrile with a minor, amount of monomeric material copolymerizable therewith, or of a blend of a major amount of such polymer or copolymers and a minor amount of a different polymer which is compatible therewith (cf. Belgian Patent No. 588,577).

At the present time, textile yarn is commercially manufactured by a method which involves continuously twisting a ribbon of cellulose paper to the extent of 5 to or more times per inch so as to form a yarn having a diameter A or less of the width of the ribbon. A twisting rate of 300 twists per minute is currently regarded as slow, and modern high-speed machines produce more than 3,000 twists per minute. Even slow twisting subjects the paper to deformation which is sufi'iciently sudden and sharp to cause the paper to crack. It is necessary, therefore, for the paper to be in limp state during the twisting step, and this is effected by pro-wetting the paper with water. t

Water is seriously detrimental to the tensile strength of cellulose paper, and therefore only wet strength paper (paper which contains a wet strength resin) is adapted to the twisting process.

Up to the present it has not proved practical to produce yarn from water-laid polyacrylonitrile'paper because polyacrylonitrile paper possesses the snap and rattle of crisp bond cellulose paper, and no means has been found for rendering the paper limp without also rendering it tacky, as for examplewhen the paper is sprayed with a solvent. Polyacrylonitriletpaper can be wet with water,

but the water does not render the paper sufficiently limp to permit it to be twisted as described.

lnathepast, it has proved possible to form yarn from polyacry'lonitrile paper ribbon without cracking the rib- V bon, by twisting the ribbon ,at very slow speeds, i.e., at speeds less than about 150 twists per minute. However,

the resulting yarn-has not proved satisfactory because polya crylonitrile paper is springy, and the resulting yarn pus-- sesses, a strong intrinsic tendencyrto .untwist. This tendency-becomes evident when the yarn breaks or is cut; in which event it instantly reverts back to paper ribbon form. i? The discovery has now been made that a continuous twisted yarnwhich has no inherent tendency to revert to We have successfully produced yarn from polyacrylonitrile paper ribbon at the rate of 3960 twists per minute, which indicates that the process can be successfully performed at the maximum rate which modern twisting machines are capable of.

The product is a continuous textile yarn consisting essentially of a heat-set twisted paper ribbon of heat-bonded fibrillated water-laid polyacrylonitrile papermaking fibers.

The invention results from the discovery that when polyacrylonitrile paper is heated momentarily above its rattle point, the fiber-to-fiber bonds of the paper remain sufiiciently strong to permit the paper to withstand the tensions involved in the twisting operation, and that this heating does not cause significant permanent detriment to the paper.

As stated, polyacrylonitrile paper normally (i.e., when dry and at room temperature) exhibits the rattle and snap characteristics of good quality bond paper. VJ e have found that when heated, however, the paper passes through a transition point above which the paper is substantially as limp as untreated cloth or wet chamois leather and does not rattle when shaken. This transition temperature (hereinafter termed the rattle point) can be determined by placing a sheet of the paper in contact with an electric hot plate having a known surface temperature, allowing the sheet to come to thermo-equilibrium, and then rapidly removing the sheet with tongs applied to one corner or end and causing the paper sheet to undergo wave-like shakes by rapidly moving the tongs to and fro horizontally while the paper is suspended vertically. When the test is repeated over a series of temperatures, the approximate I ribbon and avoids the danger of the ribbon breaking while 7 it is twisted or of yellowing or becoming tacky.

During yarn manufacture this most conveniently determined by shaking the ribbon by hand as it emerges from the heating means. The limpnes's which the paper pos sesses above its rattle point is readily perceived with a little practice. We have noticed'that a comparatively soft yarn is generally produced whenthe paper is twisted at low temperature (e'.g.150250 F.) andlthata strongerbut harsher yarn is generally obtained when the paper is ribbon form can be manufactured at commercial speed,

ie at speeds in excess of 300 twists per minute, from a 7 paperri bbon substantially composed of-heaflbonded, fibrillated water-laid polyacrylonitrile, papermaking fibers, provided thatthe twisting isperformed whilethe ribbon is at yafltemperaturejin excess of its rattle point. A faature of. i the invention is. that the resiiltin'gyarm; at room tempera- ;ture,is heat-setfa nd'possesses no tendency-.torevertjback f toi -ribbon form even whenbrok en or cu't'fandja' further feature is-that the process can be performed at high speeds.

ciently 1 at atemperature safely flbOY6" llZS. rattle point.

twisted at a higher temperature, e.g. 300400 C. The two-ranges thus produce" distinct types of yarn.

t The invention does not depend on the method employed for heating the paper ribbon to bring .it above its rattle point, and any convenient method may be employcd. One suitable methodis to subject the ribbon to direct infra red radiation. .Another method is toothploy a gas flame as the directjsou'rce of heat. still an other means is to. heat the ribbonby direct, contact with,

steam.

Inpractica 'we have found it most convenient to" em-' ploy 'asmooth electrically-heated quartz tube as the heat ing means, a thermocouple being used to determine the temperature within, anda transformer beihg p'rov-ided so that the temperature may be varied as' desired, v The ribbon is passed through the tube," and the temp 'erature I of the tube iscorrelated the speedor travel of the ribbon so thatjthetemperature of thflribbon is suffi high to ensurethat it arrives at the twisting point estimated at 300 F. within the tubes. run through the heated tubes without'being threaded 'through the traveller,.so" that no twisting occurred. As thefit'emperatureof the heating tubes increased, a'tema The resulting yarn or thread may be wound at once, and special cooling has not been found necessary. Thus the yarn may be spooled at a temperature between its rattle point and its tack point. I

The yarn produced by the process may contain some or all of the components normally found in synthetic polyacrylonitrile paper as, for example, wet-strength resins, sizing agents, and pigments and dyes, together with minor amounts of other fibers which may be cellulose papermaking fibers.

The yarn has the open, porous, fibrous structure characteristic of cotton yarn. It may be woven or knitted in normal manner to form textile fabrics. These textile fabrics, being substantially composed of polyacrylonitrile fibers, possess particular utility for applications where resistance to water, most organic solvents, ultraviolet light, and acids are desired. These textiles are therefore particularly suited for the manufacture of chemical filter cloth and outdoor apparatus coverings.

The invention does not depend upon the number of turns given the ribbon during the twisting operation. In general the ribbon is twisted so as to provide a yarn having a diameter V or less of the width of the ribbon employed.

The. invention will be more particularly illustrated by the examples which follow. These examples represent embodiments of the invention and are not to be construed as limitations thereof.

Example 1 The paper used was a water-laid web substantially composed of heat-bonded fibrillated polyacrylonitrile papermaking fibers composed of approximately 90% by weight acrylonitrile-l% methylmethacrylate copolymer. The paper had a basis weight of 35 lbs. per in. per

2 x 36"/500 ream, and was supplied as rolls of ribbon /s in. wide. This ribbon consistently broke when twisted to the extent of 3 twists per inch at the rate of 180 twists per minute (ribbon speed 5 feet per minute), but could be twisted without breaking at 120 twists per minute.

The twisting machine used was a Meadows full-scale 12-spindle paper ribbon twister, but only one spindle was used.

The machine was modified by installing two quartz heating tubes each 6". long and A in diameter for heating the paper ribbon before twisting. One tube extended upstream' from the last steel roller yarn guide located approximately 8 inches from the twisting point, and the other extended downstream from this roller guide to -the pigtail yarn guide, sothat most of the twisting occurred while the paper was passing through the latter tube. Both tubes were wound with nichror'ne electrical resistance tape and were covered with asbestos paper for thermal insulation. An infra-red lampwas positioned above the steel roller guide, over the space between the tubes, to prevent theribbon from cooling as it passed this point,

Electric current was supplied to each of the heating tubes through a variable transformer, and the transformers were gradually turned up'to develop'an air temperature The ribbon was perature was reached at which the ribbon left the second or downstream tube in limp state, showing that it was above its rattle point. At this point the ribbon was threaded through the traveller and onto the collecting spool. Additional heat was then supplied to ensure a twisting temperature safely in excess of the rattle point of the ribbon, and the twist-ing machine was placed in full operation at the rate of 3,600 twists per minute (ribbon speed 30 feet per minute; 10 twists per inch).

Yarn formation took place smoothly and without difi'iculty. The paper ribbon showed no tendency to break. The temperature of the ribbon at the point of twisting was estimated to be approximately 250 F.

The temperature of the heating tubes was varied on either side of the starting temperature. The ribbon developed a tendency to crack when twisted at a tempera ture below approximately 200 F. and the ribbon tended .to yellow and become tacky when heated above about 500600 F. The range 200 F. to 400 F. appeared to be preferable, because very satisfactory results Were obtained without any noticeable change in the color or other properties of the fibers.

Example 2 The foregoing procedure was repeated, except that the upstream heating tube and infra-red lamp were removed, and the downstream heating tube was replaced by a heating tube 3" in length so as to provide flash heating The procedure of Example 1 was repeated except that the heating tubes and the infra-red lamp were removed, and the ribbon was passed between two elongated orifices which supplied steam over a 6" length of the ribbon as close to the twisting point as possible, and an infra-red lamp was positioned to shine on the ribbon as it advanced to the twisting point, so as to prevent the ribbon from cooling prior to being twisted. Substantially the same results were obtained.

Processes for the manufacture of yarn claimed herein are disclosed and claimed in our copending divisional application Serial No. 358,106, filed on April 7,1964.

We claim:

A continuous textile yarn consisting essentially of a heat-set twisted paper ribbon of heat-bonded fibrillated water-laid polyacrylonitrile papermaking fibers,the diameter of said yarn being less than about of the width of said ribbon.

References Cited in the file of this patent UNITED STATES PATENTS 

